Spatially resolved detection of complex ferromagnetic dynamics using optically detected nitrogen-vacancy spins

Abstract

We demonstrate optical detection of a broad spectrum of ferromagnetic excitations using nitrogenvacancy (NV) centers in an ensemble of nanodiamonds. Our recently developed approach exploits a straightforward CW detection scheme using readily available diamond detectors, making it easily implementable. The NV center is a local detector, giving the technique spatial resolution, which here is defined by our laser spot, but in principle can be extended far into the nanoscale. Among the excitations we observe are propagating dipolar and dipolar-exchange spinwaves, as well as dynamics associated with the multi-domain state of the ferromagnet at low fields. These results offer an approach, distinct from commonly used ODMR techniques, for spatially resolved spectroscopic study of magnetization dynamics at the nanoscale.PACS numbers: 07.79.-v, 72.25.-b, 85.75.-d Spintronic [1,2] and magnonic devices [3][4][5] are receiving intense scientific attention due to their promise to deliver new technologies that can revolutionize computing and provide greater energy efficiency. In particular, tools for understanding phenomena such as angular momentum transfer across interfaces [6][7][8][9][10], spin wave propagation in low dimensional and nanoscale systems [11,12], domain wall motion [13][14][15], microwaveassisted switching [16], and relaxation and damping in small structures [17] are needed. There is current interest in materials with more novel magnetic textures than simple ferromagnets, such as skyrmions [18]. Electrical detection has been widely used for studying domain wall motion, but does not have imaging capabilities. Optical techniques such as Brillouin light scattering (BLS) [12] and the magneto-optic Kerr effect (MOKE) [19] are also widely used but are ultimately limited by the optical diffraction limit. Scanned probe techniques can provide high spatial resolution but can be perturbative and may require a more challenging set-up such as vacuum and cryogenic environment to achieve high sensitivity.Nitrogen-vacancy (NV) centers in diamond have emerged as an attractive tool to study magnetic phenomena at the nanoscale, and they offer a way to convert magnonic signals into optical signals. NV centers offer a powerful magnetometry tool due to a potent combination of optical and magnetic properties that make the intensity of their photoluminescence (PL) dependent on their spin state. This has allowed detection of just a few resonant nuclear spins and nuclear magnetic resonance imaging with resolutions of tens of nanometers, all under ambient conditions and at room temperature [20][21][22]. NV centers have also been used to study domain wall hopping [23], the helical phase in FeGe [24], * hammel@physics.osu.edu* † bhallamudi.1@osu.edu* and spinwave modes in permalloy [25]. High sensitivity to detect dynamic fields has been achieved by finding optimal NV centers with long lifetimes and manipulating them (and sometimes the target spins) with intricate microwave and optical pulse sequences.We have recently demonstrated a ne...

Broadband electron paramagnetic resonance spectroscopy in diverse field conditions using optically detected nitrogen-vacancy centers in diamond

“…We refer to the sensing protocol as NV-based Non-Resonant Broadband (NV-NRB) detection to highlight the freedom from the need for spectral overlap between the spin transitions for P1 target and NV sensor spins. Absence of spectral overlap is similar to the case of non-resonant coupling seen in NVferromagnet systems to detect ferromagnetic resonance [12][13][14]. However, we postulate a different microscopic mechanism for NV sensitivity to P1 resonances that relies on interaction with the phonon bath, in contrast to the spinwavebased mechanism for the ferromagnetic case.…”

Probing condensed matter physics with magnetometry based on nitrogen-vacancy centres in diamond

“…This phenomenon provides a convenient new technique for broadband detection of spin-wave resonances, which does not rely on matched ESR and ferromagnetic resonance (FMR) frequencies. This technique was used to study the rich ferromagnetic resonance modes of μm-thick YIG films 111 . Further experiments 109,112 unravelled the mechanism underlying this FMR-drive-induced noise, showing that FMR driving generates high-energy spin waves that can be resonant with the NV ESR frequency, thereby inducing NV spin relaxation and suppressing the NV photoluminescence.…”

Long-range spin wave mediated control of defect qubits in nanodiamonds

“…13,14 In particular, a growing body of research has focused on the interplay between the optically addressable nitrogen-vacancy (NV) center in diamond and spin wave (SW) excitations in extended ferromagnetic materials. [15][16][17][18][19] These systems have been proposed, for instance, as a platform to enable long distance coupling between NV centers, 15 by taking advantage of the SW's long damping length and the large interactions achievable through the ferromagnet's (FM) sizeable magnetization.…”

“…However, a number of recent works [16][17][18][19][20] revealed that the coherences of NV centers placed in proximity of a FM are strongly quenched by the magnetic field noise generated by driven ferromagnetic resonances. These results are of great interest for the implementation of broadband magnetic field sensing and for the study of the spin properties of ferromagnetic systems, but also suggest that incoherent mechanisms dominate the SW-NV center coupling.…”